Given its high refractive index, lack of absorption of visible light, ability to be produced at a specified size, stability and nontoxicity, pure titanium dioxide is frequently used as a white inorganic pigment. However, irregularities in the crystal lattice correspond to variations in pigment characteristics. For example, while TiO.sub.2 is white, TiO.sub.1.9995 is blue. And different oxides also correspond to variations in pigment characteristics. In particular, TiO is golden yellow, whereas Ti.sub.2 O.sub.3 is violet.
Titanium dioxide may be used with other components to make a Complex Inorganic Color Pigment (CICP). A CICP is a pigment made by heating a number of different metal oxides. When titanium dioxide is used in CICP formulations, an initial composition containing either calcined titanium dioxide or calcined titanium hydrolysate and other metal oxides is heated. However, there are drawbacks associated with using titanium dioxide or titanium hydrolysate as starting materials in CICP formulations.
Titanium dioxide occurs in nature in three crystalline forms; namely, anatase, brookite and rutile. Although the heated CICP final CICP composition contains titanium dioxide in the rutile form, it is desirable to begin with calcined anatase titanium dioxide (in the initial CICP formulation). This is because calcined anatase titanium dioxide leads to better pigment properties. However, in order to prevent conversion of anatase titanium dioxide into the thermodynamically stable rutile titanium dioxide during precalcining, it is necessary to use a rutile inhibitor. And subsequently, when the CICP formulation is heated, it is necessary to use a rutile promoter to maximize the amount of rutile titanium dioxide formed in the final CICP composition. Use of a rutile inhibitor and rutile promoter is expensive due to the requirement of additional chemicals, more complicated due to requirement of additional processing steps, and undesirable due to poor color control associated with additional chemicals in the CICP formulation.
The use of titanium hydrolysate (hydrated titanium dioxide) in CICP formulations also involves the necessity of including a rutile inhibitor and rutile promoter. This is because from 0.1 to 5% of the initially calcined titanium hydrolysate forms rutile titanium dioxide without a rutile inhibitor. Accordingly, the drawbacks attributable to the expensive and complicated nature of rutile inhibitor/promoter usage are similarly associated with titanium hydrolysate.
When making an initial CICP formulation, it is desirable to prepare alkali metal free formulations. Trapped sodium and potassium undesirably cause sintering when the CICP formulation is heated. Sintering promotes the undesirable formation of coarse aggregate particles which are difficult or impossible to grind. Relatively large, coarse, and/or hard particles often lead to problems in CICP applications. For instance, relatively large, coarse, and/or hard particles tend to cause tears and/or rips in plastic films containing such CICP particles.